Conventionally, as disclosed in International Publication WO 2003/51784, a scribing wheel is constructed of, as a base material, a disc made of a cemented carbide or polycrystalline sintered diamond (hereafter referred to as “PCD”). PCD is a substance resulting from the sintering of diamond particles together with cobalt or the like. The scribing wheel has a V-shaped cutting edge at its periphery, which is formed by cutting the circumferential edge of the disc base material at a bevel so as to provide oppositely inclined surfaces. The thusly configured scribing wheel is attached for axial rotation to a scribing head or the like of a scribing apparatus, and is pressed against a substrate made of a brittle material under a predetermined load while being moved over the plane of the brittle material-made substrate. In this way, the substrate can be scribed.
The conventional-type scribing wheel made of polycrystalline sintered diamond (PCD) is composed of diamond particles and bonding materials. Thus, the scribing wheel incurs the drawback of having a short operating life especially when it is used for scribing on a brittle material-made substrate which is higher in hardness than glass, such as ceramic substrates, sapphire substrates, and silicon substrates. It is noted that ceramic substrates include substrates having built-in electronic components, such as a multilayer substrate made of high-temperature co-fired ceramic (HTCC substrate) and a multilayer substrate made of low-temperature co-fired ceramic (LTCC substrate). As another drawback of the conventional-type scribing wheel, even if the cutting edge is ground, the roughness of its ridge line cannot be reduced satisfactorily.
Therefore, when the scribing wheel is used for scribing on a brittle material-made substrate under an unduly large scribing load, after the breaking of the scribed substrate, the end face of the segmented substrate may suffer lack of strength.